There are many different techniques for measuring characteristics of samples such as, for example, semiconductors. One such technique is ellipsometry, in which the polarization change of a light beam is measured when the light beam is reflected by the sample. This change in polarization is then related to characteristics of the sample. Ellipsometry is generally used for transparent materials, but may also be used for very thin, opaque films.
Another technique is optical stress generation and detection. This technique is described, e.g., in Maris et al., “Optical Stress Generator and Detector”, U.S. Pat. No. 5,748,318, May 5, 1998, and Humphrey Maris, “Optical Method for the Characterization of Laterally-Patterned Samples in Integrated Circuits”, U.S. Pat. No. 6,321,601, Nov. 27, 2001. These references contain detailed information about optical stress generation and detection for characterization of samples and should be consulted for their disclosure of optical stress generation and detection. Briefly, in optical stress generation and detection, a “pump” beam is used to perturb the sample, and a “probe” beam is used to analyze results of the perturbation. For instance, the pump beam could generate a stress wave that causes properties of a layer on the sample to change, and the probe beam is used to analyze the property changes. The resultant property changes are then used to determine characteristics of, e.g., the layer. Optical stress generation and detection may be used on opaque materials.
While both ellipsometry and optical stress generation and detection are useful analysis techniques, systems using these techniques could be improved.